This Eurasian biennial or sometimes winter annual weed stands 2 1/2 to 3 1/2 feet (0.75-0.9 m) tall, but may grow to 6 feet (1.8 m) tall.
The leaves are dark green with a light green central vein, deeply cut lobes and a spiny edge. The narrow leaves are up to eight inches (20 cm) long, alternately arranged and directly attached to the stem.
Single flower heads grow on the ends of long stalks, are 1 1/2 to 3 inches (4 to 8 cm) in diameter, and usually bent over at the neck. The flowers are deep rose, violet or purple, and occasionally white. They have broad, spine-tipped bracts at their base, the bottom row or two of which are bent under or recurved
The fruits are 3/16 inch (5 mm) long, shiny and yellowish-brown with a plume of white hair 3/4 inch (2 cm) long at one end.
Musk thistle was introduced to the U. S. in the early part of the century. This native of Southern Europe and Western Asia has spread throughout the U.S. and Canada. It invades pastures, wildlands, grain fields, ditch banks, roadsides, waste areas, and stream banks. In Nevada, this plant is found along roadsides, riparian areas and cultivated pastures. It spreads rapidly and forms dense stands which crowd out other plants. Tillage cuts the roots which resprout and is not recommended for control. The introduced musk thistle weevil feeds on the seeds and limits the spread of this weed.
Musk thistle seedlings have yellow spines on lobed margins.
Flowering occurs at the end of summer.
Flowers are deep rose and up to 3 inches wide. Bracts under the flower are large, pointed and the bottom row or two turn under.